1. Field
The disclosed embodiments concern a lightning protection system for a composite structure, particularly panels with a light central core, such as a honeycomb core. It is specially adapted for lightning protection on a radome or aircraft fuselage.
2. Brief Description of Related Developments
Sandwich structures made of composite material have exceptional properties, especially mechanical ones. They combine high resistance to mechanical and/or thermal stresses with strong rigidity at minimal weight.
These structures are therefore widely used in the space industry (satellites, probes, launchers) and in the aeronautics industry (radomes, hatches, leading edges, ailerons, etc. . . . ).
However, it is known that these structures are vulnerable to lightning strikes if they are not properly connected to the ground. High-density electric currents passing through these composite structures can severely damage them and result in delamination, for example. The case of the radome is even more critical, since, by definition, it cannot have the traditional devices to carry the lightning current, such as a metal grill inserted in the surface of the structure, because radar waves require transparency.
There are known means of dissipating the energy from lightning to protect these structures in the event of a lightning strike.
FIG. 1 shows such a means of dissipating the energy from lightning from the prior art. Lightning-protection strips 1, typically made of aluminum or copper, are located on the outer surface 2 of an aircraft radome 3. These strips 1 are attached to the radome by screw-type fasteners 4. Each lightning-protection strip 1 is electrically connected to the outer surface 2 of the radome 3, so the electrostatic charges that accumulate there can flow off. Part 5, into which the screw 4 to attach the strip 1 fits, is made of insulating plastic.
Each strip 1 is also connected to the junction of the aircraft fuselage to make sure it is individually grounded. Thus, a lightning bolt that strikes this strip 1 has its energy diverted to the ground without affecting any other part of the radome.
Although this means of dissipating energy gives good results, interference 6 with the incident air flow 7 on the radome 3 has been observed; it is caused by the projections formed by the lightning-protection strips 1 on the outer surface 2 of the radome (FIG. 1b).
When the radome forms the “nose” of an airplane, it is generally conical in shape to give the aircraft good air penetration and aerodynamics.
This aerodynamic interference 6 generates increased drag, particularly by triggering a transition from laminar to turbulent flow, and it also substantially increases the aircraft's fuel consumption, which is incompatible with the economics of the airline companies.
When lightning strikes a lightning-protection strip hard, it is possible for it to be damaged, for example when there is superficial melting of the screw attached to the strip. During radome maintenance, it must then be taken out to remove and replace the damaged strip.
It would therefore be of interest to have a system to protect the radome of an aircraft from lightning that would also make it possible to reduce drag, gain fuel weight and be as transparent to radar waves as possible.